The present invention relates to a heat spreader for semiconductor devices with excellent heat dissipation and a small difference in thermal expansion from an Si chip without peeling from a resin or ceramic package even at larger heat generation due to higher integration of chip circuits, a semiconductor device including such a heat spreader, and a method for producing such a heat spreader.
Since more and more heat is generated from semiconductor devices due to increasingly higher integration of circuits, semiconductor devices are provided with heat spreaders to dissipate heat therefrom. A typical example of such semiconductor devices is shown in FIGS. 1-5. FIG. 1 shows a semiconductor device in which a silicon chip 1 is bonded to a heat spreader 2 with a bonding material layer 6 and embedded in a resin (plastic) 8. A plurality of leads of the semiconductor device are connected to a circuit board 10 via a solder layer 9. The heat of the silicon chip 1 is conducted to the heat spreader 2 via a bonding material layer 6 made of a silver paste, etc. and dissipated to the circuit board 10 via a bonding material layer 7 and an inner lead portion 3a and an outer lead portion 3b of each lead. The heat spreader 2 may also be called "heat sink" or "header."
FIG. 2 shows a semiconductor device having a resin 8 from which a heat spreader 2 is exposed to perform heat dissipation. FIG. 3 shows a semiconductor device provided with a heat spreader 2 having a heat dissipation fin member 12 bonded thereto by a bonding material layer 11 to exhibit increased heat dissipation. In the semiconductor device structures described above, the circuits on the silicon chip 1 are connected to an outside circuit board 10 via bonding wires 5, and inner lead portions 3a and outer lead portions 3b of lead frame 3.
FIG. 4 shows an example of a ball grid array (BGA) type plastic package. A circuit of a printed circuit board substrate 13 is connected to a silicon chip 1 via bonding wires 5 and also is connected to an outside circuit via ball bumps 14. Bonding wires 5 are sealed by a resin 8. A heat generated from the silicon chip 1 is dissipated from a heat dissipation fin member 12 via a heat spreader 2. FIG. 5 shows an example of a ceramic package for a silicon chip. The silicon chip 1 is connected to pins 17 mounted to a ceramic substrate 15 via bonding wires 5, and the pins 17 are connected to an outside circuit. The bonding wires 5 are protected by a cap 16. A heat generated from the silicon chip 1 is dissipated from a heat dissipation fin member 12 via a heat spreader 2.
In various types of semiconductor devices as described above, the heat spreaders 2 are preferably made of materials having high thermal conductivity. A more important factor for the heat spreaders 2 is a thermal expansion coefficient. Accordingly, in actual semiconductor devices, materials for heat spreaders are selected from metals and sintered metals having low thermal expansion coefficients close to that of Si depending on the types of the semiconductor devices, taking into account thermal strain in a solder reflow treatment during the mounting process and in a T cycle heat hysteresis test at a temperature of from -55.degree. C. to +150.degree. C. In semiconductor devices with plastic packages, 42% Ni--Fe alloy (42 alloy) is widely used for heat spreaders. In semiconductor devices with ceramic packages, sintered metals of Cu--Mo, Cu--W, Mo, etc. are used for heat spreaders. These materials, however, are poor in machinability and platability and disadvantageous in cost and weight.